Transcript Chapter 40 Subclass Acari: Ticks and Mites

Chapter 40
Subclass Acari:
Ticks and Mites
Morphology
• The main tagmata of this group are the prosoma and opisthosoma)
• The gnathostoma (capitulum) bears 3 structures that make up the
mouthparts: the hypostome, a pair of chelicerae, and the pedipalps
• Mouthparts of the Acari are modified for specialized feeding
Morphology cont.
•Among ticks, the pedipalps grasp a skin, while the chelicerae cut through
it; the hypostome is thrust into the wound and the teeth anchor the tick
• During feeding, the pedipalps either bend outward (soft ticks) as the
chelicerae and hypostome penetrate the flesh or remain rigidly and
intimately associated with the hypostome (hard ticks) during skin
penetration; the pedipalps serve as counter-anchors while the tick is
attached to the host
• Mites have small mouthparts and often feed on lymph and other
secretions that are produced once the chelicerae bite the tissue; hypostome
lacks teeth and therefore does not serve as an anchor
Mite capitulum
Tick capitulum
Morphology cont.
• Mites and ticks possess 3 pairs of walking legs as larvae and 4 pairs as
nymphs and adults
• Leg is divided into 6 segments: coxa, trochanter, femur, tibia, pretarsus
and tarsus (usually the tarsus terminates in a claw)
Differences between Ticks and Mites
Ticks
Large; macroscopic
Toothed hypostome
Haller’s organ present
(on 1st tarsi; olfaction)
Mites
Smaller; microscopic
Hypostome unarmed
Haller’s organ absent
Order Ixodida - Ticks
Three families are recognized:
 F. Argasidae (soft ticks) – flexible,
tough, bulbous bodies that obscure
the mouthparts and most of the legs
• F. Nutalleidae – are rare African
family consisting of a single species,
which is somewhat intermediate
between the soft ticks and the hard
ticks
 F. Ixodidae (hard ticks) – which
have a dorsal sclerotized plate
(=scutum), and a conspicuous
gnathostoma projecting in front of
the body
Argas
Amblyoma americanum
Soft Tick Life Cycle
• Soft ticks are thought to be a more primitive group: they may have
more than one larval stage and 2 or more nymphal stages
• Soft ticks are often nest parasites; they feed quickly and repeatedly
on the same animals and usually return to their resting-place between
meals
Hard Tick Life Cycle
• Hard ticks have a more rigid life cycle; they have a single larval and
nymphal stage
• Most engorge 3 time during their life; unlike soft ticks, they remain attached
to the host and feed and engorge for extended periods of time
• Typically a larva attacks one animal, attaches, engorges, leaves the animal,
molts to the nymphal stage, attacks a second host, attaches, engorges, leaves
that animal, molts to the adult stage, and attacks a third host
• Males copulate with females on
the 3rd host but do not engorge
• Females attach for a few days,
engorge and leave the host to lay a
single clutch of eggs, after which
they die
Hard Tick Life Cycle cont.
• Most ticks are intermittent parasites
of mammals, birds and reptiles;
however, they usually demonstrate
little host specificity
• When seeking a host, hard ticks
usually climb on vegetation and adopt
a posture known as “questing”
• Both sexes of ticks are bloodsuckers, although adult males take
little blood
• Before or during engorgement, the
female hard tick is inseminated by the
male; spermatophores are introduced
into the vagina by the gnathostoma of
the male
Questing behavior
Tick-Borne Illnesses and Diseases
Pathogenesis attributable to ticks can be categorized as follows:
• Anemia. Blood loss due to heavy infections
• Dermatosis. Inflammation and itching from a tick bite; due to tick
mouthparts, saliva, and bacterial infections
• Paralysis. Due to the realease of toxic secretions when persons are
bitten at the base of the skull
• Otoacariasis. Infestation of the inner ear canal by ticks that causes
irritation and sometimes secondary infection
• Infections. Ticks transmit viruses, bacteria, rickettsisa, protozoa, etc.
O. Mesostigmata
• These mites have a pair of
respiratory spiracles, stigmata,
that are located just behind and
lateral to the 3rd coxa
• Extending anteriorly from each
stigma is a tracheal trunk,
peritreme
• The gnathosoma forms a tube
surrounding the mouthparts; a
bristlelike tritosternum is
usually present just behind the
gnathosoma
• The dorsum of adult usually has
one or two sclerites called dorsal
plates
O. Mesostigmata cont.
• One example from this order is the chicken mite, Dermanyssus
gallinae that attacks chickens and pigeons
• Often occur in the nests and feed on their hosts at night; heavy
infestations may cause the fowl to abandon the nest
• This mite can attack humans and cause severe dermatitis
• Also, this mite is known to carry western equine encephalitis
Dermanyssus
O. Prostigmata
• Some spiracles near and associated with
the gnathosoma; weakly sclerotized
• Include the chiggers from the F.
Trombiculidae
• Chiggers are the parasitic larval stage of
trombiculid mites, attacking mammals,
birds, reptiles and amphibians; nymphs and
the adults are predacious, feeding on small
arthropods
• When chiggers feed on a vertebrate host, their salivary secretions harden in
the skin to form a tube called a stylostome through which the fluids or
digested tissues of the host pass
• Feeding of some chiggers, especially of the genus Eutrombicula, causes an
intense irritation of the skin; scratching of the feeding sites produces sores
that often become infected with bacteria
O. Prostigmata cont.
• Larvae are vectors of scrub typhus, a rickettsial disease in humans
• Also includes the follicular mites in the F. Demodicidae
• Two species are found in man: Demodex folliculorum in hair follicles and
D. brevis in sebaceous glands
• Both exist mainly on the face, particularly around the nose and the eyes
• All life stages may be found on a single follicle
O. Orbatida
• These are beetle-like free-living mites
• They live in the soil and the vegetation and are commonly ingested
by sheep and other grazing animals
• They serve as intermediate hosts for some trematodes that run
through sheep (e.g., Moniezia expansa)
The beetle mite Oppia
O. Astigmata
• Lack a tracheal system with spiracles; respire through the tegument
• They lack tarsal claws; have sucker-like structures in their place
• The infestation of animals by mites is known as mange
O. Astigmata cont.
•The best known astigmatid mites are of the F. Sarcoptidae
• The mite Sarcoptes scabiei is responsible for sarcoptic mange or
scabies
• Mating occurs on skin; female mites burrow in the skin, laying 2 or 3
eggs a day as she burrows; males remain on skin surface
• The immature stages emerge from the burrows and transfer to new
hosts
• Mites causes a severe irritation to
the skin and the awakened host
scratches, further irritating the skin
and in some cases causing
secondary infection
• Transmission of the disease is by
contact, adult females being passed
from one host to another
Sarcoptes scabiei
O. Astigmata cont.
• “Scab” in sheep or cattle is caused by
non-burrowing mites of the F. Psoroptidae
• The males are smaller than the females
and have prominent anal suckers and
reduced hindlegs
• Mites of the genus Psoroptes produce
important diseases in sheep, cattle and
rabbits
• The mites are found on the surface of the
body among the scabs at the base of the
hairs
(Psoroptes equi)
O. Astigmata cont.
Other Examples include:
Acarapsis or tracheal mites
Dermatophagoides or dust mites;
most are non-parasitic, with people
being allergic to their feces